Internal combustion engine with exhaust-gas aftertreatment arrangement and method for operating an internal combustion engine of said type

ABSTRACT

A system and method for controlling temperature of a urea reductant to form ammonia for NOx reduction in a selective catalytic reducer coupled to a turbocharged engine exhaust by portioning a flow across the reductant between compressed air and ambient air.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German Patent Application No.102013202496.7, filed on Feb. 15, 2013, the entire contents of which arehereby incorporated by reference for all purposes.

BACKGROUND Summary

An internal combustion engine with an exhaust gas after-treatment systemcomprising a selective catalytic reducer (SCR) catalyst is commonly usedto treat NOx emissions. A reductant, often aqueous urea, is injected viaa dosing device in the exhaust line upstream of the SCR catalyst. TheNOx reacts with the reductant to form byproducts such as water andnitrogen.

One example approach positions the dosing device upstream of the SCRcatalyst in an exhaust bypass line. A control valve is positioned in theexhaust bypass line to control the volume flow of exhaust through thebypass line to control the temperature of the hydrolysis catalyst.Another example approach is to use HC enrichment by introducing unburnedhydrocarbons directly into the exhaust-gas discharge system to act asthe reductant by means of post-injection of additional fuel into acombustion chamber.

A potential issue noted by the inventors with the use of a control valvein the exhaust bypass line is the relative complexity of the system andthe temperature control and selected mass flow limitations of using avalve positioned in the exhaust bypass line. Further, there may beoperating conditions under which reductant may not be delivered to theSCR catalyst and allow the release of NOx. Another potential issue notedby the inventors is with HC enrichment which utilizes post-injection.The internal combustion engine may be susceptible to thinning orcontamination of the oil with unburned hydrocarbons. Further, additionalfuel is used as the reducing agent thereby increasing overall fuelconsumption.

One potential approach to at least partially address some of the aboveissues includes an internal combustion engine comprising an intakesystem for the supply of charge air and an exhaust gas discharge systemfor the discharge of the exhaust gases. Further at least one selectivecatalytic converter is arranged in the exhaust gas discharge system forthe reduction of nitrogen oxides wherein an oxidation catalyticconverter being arranged as a further exhaust gas after-treatment systemupstream of the at least one selective catalytic converter. A bypassline branching off from the intake system and issuing into the exhaustgas discharge system between the oxidation catalytic converter and theat least one selective catalytic converter further comprising a dosingdevice being provided for introducing liquid urea as a reducing agentfor the at least one selective catalytic converter into the bypass line.

Another potential approach to at least partially address some of theabove issues includes a method for operating an internal combustionengine having a control element for the adjustment of the air flow rateconducted through the bypass line wherein the bypass line is opened inorder to supply ammonia as the reducing agent to the at least oneselective catalytic converter.

Another potential approach includes a method for controlling an enginewith a selective catalytic reducer coupled to the engine exhaustcomprising supplying compressed air to the engine to achieve a selectedtorque and injecting a reductant into the SCR. The temperature of thereductant may be controlled within a predetermined range by portioningan air flow into said reductant between a portion of said compressed airand ambient air. Further, the engine torque may be adjusted tocompensate for said portioning of said compressed air.

Another potential approach further includes a method for maintainingtemperature of the dosing device within a selected range, whilemaintaining emissions control and operating the engine at a selectedpower output. The method comprises supplying compressed air to theengine to achieve a selected torque, injecting a reductant into theselective catalytic converter, and controlling temperature of thereductant within a predetermined range by portioning an air flow intothe reductant between a portion of the compressed air and ambient air.The method may further adjust engine torque to compensate for theportioning of the compressed air. The compressed air may be suppliedfrom a compressor driven by a turbine positioned in the engine exhaustdischarge system.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 schematically shows, in the form of a diagrammatic sketch, afirst embodiment of the internal combustion engine.

FIG. 2 schematically shows, in the form of a diagrammatic sketch, asecond embodiment of the internal combustion engine.

FIGS. 3 a and 3 b show an example method to operate an internalcombustion engine according to the first or second embodiment.

FIG. 4 schematically shows, in the form of a diagrammatic sketch, thefirst embodiment combined with an exhaust bypass line.

FIG. 5 schematically shows, in the form of a diagrammatic sketch, thesecond embodiment combined with an exhaust bypass line.

FIGS. 6 a, 6 b and 6 c show an example method to operate an internalcombustion engine as shown in FIG. 4 or 5.

DETAILED DESCRIPTION

The present application relates to an internal combustion engine whichhas an intake system for the supply of charge air and has an exhaust-gasdischarge system for the discharge of the exhaust gases and has at leastone selective catalytic converter which is arranged in the exhaust-gasdischarge system and which serves for the reduction of nitrogen oxides,an oxidation catalytic converter being arranged, as a furtherexhaust-gas aftertreatment system, in the exhaust-gas discharge systemupstream of the at least one selective catalytic converter.

The present application also relates to a method for operating aninternal combustion engine of the above-stated type. An internalcombustion engine is used for example as a drive of a motor vehicle.Within the context of the present application, the expression “internalcombustion engine” encompasses diesel engines and applied-ignitionengines and also hybrid internal combustion engines, which utilize ahybrid combustion process, and hybrid drives which comprise not only theinternal combustion engine but also an electric machine which isconnected in terms of drive to the internal combustion engine and whichreceives power from the internal combustion engine or which, as aswitchable auxiliary drive, outputs additional power.

According to the prior art, to reduce the pollutant emissions, internalcombustion engines may be equipped with various exhaust-gasaftertreatment systems.

In applied-ignition engines, use is made of catalytic reactors which,through the use of catalytic materials which increase the rate ofcertain reactions, better enable an oxidation of HC and CO even at lowtemperatures. To additionally reduce nitrogen oxides NOx, this may beachieved through the use of a three-way catalytic converter,stoichiometric operation (λ≈1) of the applied-ignition engine within anarrow threshold. Here, the nitrogen oxides NO_(x) may be reduced bymeans of the non-oxidized exhaust-gas components which may be present,specifically the carbon monoxides CO and the unburned hydrocarbons HC,wherein said exhaust-gas components may be oxidized at the same time.

In internal combustion engines which may be operated with an excess ofair, for example direct-injection diesel engines or lean-burnapplied-ignition engines, the nitrogen oxides NO_(x) in the exhaust gascannot be reduced out of principle, that is to say on account of thelack of reducing agent.

For this reason, it is necessary to provide an exhaust-gasaftertreatment system for the reduction of the nitrogen oxides, forexample a selective catalytic converter, also referred to as SCRcatalytic converter, in which reducing agent is introduced into theexhaust gas in a targeted manner in order to selectively reduce thenitrogen oxides. As reducing agent, in addition to ammonia NH₃ and urea,use may also be made of unburned hydrocarbons. The latter is alsoreferred to as HC enrichment, with the unburned hydrocarbons beingintroduced directly into the exhaust-gas discharge system or else bymeans of engine-internal measures, for example by means of apost-injection of additional fuel into the combustion chamber. Here, thepost-injected fuel should not be ignited in the combustion chamber bythe main combustion which is still taking place or by the—even after theend of the main combustion—high combustion gas temperatures, but rathershould be introduced into the exhaust-gas discharge system upstream ofthe selective catalytic converter during the charge exchange.

Internal combustion engines which utilize post-injection may beinherently susceptible to thinning or contamination of the oil withunburned hydrocarbons. Depending on the post-injected fuel quantity andthe injection time, a greater or lesser fraction of the post-injectedfuel impinges on the cylinder internal wall, mixes there with theadherent oil film, and thus contributes to the thinning of the oil.Furthermore, out of principle, the use of additional fuel as reducingagent increases the overall fuel consumption of the internal combustionengine.

Therefore, for the reduction of nitrogen oxides, use is increasinglybeing made of selective catalytic converters in which ammonia or urea isprovided as reducing agent.

Owing to the toxicity of ammonia NH₃, ammonia is generally not stored inmotor vehicles, or provided as reducing agent, in pure form. Rather,urea is often used as a precursor product for the production of ammonia,because urea can, with a supply of energy, be split into ammonia andisocyanic acid in a thermolytic reaction, wherein ammonia NH₃ can beobtained again from the isocyanic acid in the presence of water.

In the case of urea being provided for producing ammonia, it is possibleto make a distinction between two approaches which differ fundamentallyfrom one another. On the one hand, the urea may be stored and providedin liquid form, which is to say as an aqueous solution, the urea beingintroduced as aqueous solution into the exhaust gas upstream of theselective catalytic converter. On the other hand, it is possible for theurea to be provided in solid form. Urea in solid form takes up lessvolume and is characterized by a higher ammonia content in relation tothe aqueous solution. The storage vessel can therefore be formed with asmaller storage volume, which is a significant advantage in particularwith regard to use in motor vehicles, in which it is sought to achievethe densest and most effective packaging possible.

Both concepts introduce heat into the urea in order to produce ammonia.This may pose potential issues in certain operating modes. For example,if an aqueous urea solution is introduced into the exhaust gas upstreamof a selective catalytic converter, exhaust-gas temperatures ofapproximately 150° C. to 170° C. may be necessary to evaporate the ureasolution, produce ammonia NH₃ and adequately mix said ammonia, whichserves as reducing agent, with the exhaust gas such that as homogeneousas possible an exhaust-gas/ammonia mixture is formed and flows throughthe catalytic converter.

In the case of diesel engines, in inner-city traffic, difficulties canbe encountered in generating or attaining exhaust-gas temperatures ofthe above-mentioned magnitude. It must be considered here that,normally, exhaust-gas temperatures of only 100° C. may be attained atidle, and internal combustion engines require a certain warm-up phaseafter a cold start in order for the individual exhaust-gasaftertreatment systems to reach their operating temperature and convertpollutants.

Selective catalytic converters can not only reduce nitrogen oxides inthe presence of a reducing agent, for example ammonia, but in thepresence of suitable temperatures can also absorb and store ammonia andrelease said ammonia again for the reduction of nitrogen oxides. To beable to absorb ammonia, certain minimum temperatures of the catalyticconverter may be considered. In general, catalytic convertertemperatures of between 180° C. and 300° C. may be sought in order tobetter enable satisfactory exhaust-gas aftertreatment by means of an SCRcatalytic converter.

The statements made above give the impression that it is advantageousfor selective catalytic converters to be arranged as close as possibleto the outlet of the internal combustion engine, that is to say in aclose-coupled position, in order that the exhaust gases may be givenlittle time and opportunity to cool down and in order to better enablethat the catalytic converter reaches its operating temperature asquickly as possible, in particular after a cold start of the internalcombustion engine.

Here, however, it must be borne in mind that an internal combustionengine generally has further exhaust-gas aftertreatment systems, theclose-coupled arrangement of which may be of even greater relevance. Forexample, an oxidation catalytic converter is commonly arranged as afirst exhaust-gas aftertreatment system in the exhaust-gas dischargesystem, which oxidation catalytic converter serves to oxidize theincompletely burned combustion products, specifically the carbonmonoxides CO and the unburned hydrocarbons HC. Here, a close-coupledarrangement of the oxidation catalytic converter is essential in orderthat, in particular, the untreated emissions of carbon monoxide andunburned hydrocarbons, which may be high after a cold start, may belowered in an effective manner and fast heating of the oxidationcatalytic converter after a cold start is better enabled.

If a regenerative particle filter is used for the reduction of the sootparticle emissions, high temperatures of approximately 550° C. may beconsidered for the regeneration of the particle filter if catalyticassistance is not provided, such high temperatures being attained duringoperation only at high loads and at high engine speeds. As close-coupledan arrangement as possible is thus also expedient with regard to aparticle filter.

It must also be considered that a selective catalytic converter releasesabsorbed ammonia at very high catalytic converter temperatures aboveapproximately 400° C., without nitrogen oxides being reduced. Both thereleased ammonia and also the untreated, nitrogen-oxide-containingexhaust gas may be then discharged via the exhaust-gas discharge systeminto the environment.

Even though the present regulations do not imperatively require on-boarddiagnosis (OBD), future limit values for nitrogen oxide emissionsprescribed by legislators could make this necessary. For example, theEURO VI regulation prescribes the monitoring of nitrogen oxide untreatedemissions. In particular, on-board diagnosis (OBD), specifically themonitoring of the ammonia concentration in the aftertreated exhaust gas,could become essential for reliably reducing ammonia from beingintroduced into the environment.

The technical relationships described above make it clear that conceptsmay be considered which enable selective catalytic converters to beoperated in optimum fashion with regard to the most effective possibleexhaust-gas aftertreatment of an internal combustion engine. Suchconcepts should in particular be able to influence the exhaust-gastemperature of the exhaust gas to be treated, and thus the temperatureof the catalytic converter, in order to better enable high-qualityexhaust-gas aftertreatment, that is to say an effective reduction ofnitrogen oxides.

Against the background of that stated above, it is an object of thepresent application to provide an internal combustion engine which isoptimized with regard to the operation of the at least one selectivecatalytic converter.

It is a further sub-object of the present application to specify amethod for operating an internal combustion engine of said type.

The first sub-object is achieved by means of an internal combustionengine which has an intake system for the supply of charge air and hasan exhaust-gas discharge system for the discharge of the exhaust gasesand has at least one selective catalytic converter which is arranged inthe exhaust-gas discharge system and which serves for the reduction ofnitrogen oxides, an oxidation catalytic converter being arranged, as afurther exhaust-gas aftertreatment system, in the exhaust-gas dischargesystem upstream of the at least one selective catalytic converter,wherein a bypass line branches off from the intake system and issuesinto the exhaust-gas discharge system between the oxidation catalyticconverter and the at least one selective catalytic converter, a dosingdevice being provided for introducing liquid urea as a reducing agentfor the at least one selective catalytic converter into the bypass line.

In the case of the internal combustion engine, it is possible for theselective catalytic converter to be impinged on directly with a carriergas stream for the reducing agent, specifically an air stream, whilefurther exhaust-gas aftertreatment systems situated upstream of thecatalytic converter may be bypassed. Here air may be conducted directlyto the selective catalytic converter, past the further exhaust-gasaftertreatment systems, via a bypass line.

By means of said measure, the opening of the bypass line for the passageof air, that part of the exhaust-gas discharge system which is situatedbetween the outlet of the internal combustion engine, that is to say theoutlet openings of the cylinders, and the selective catalytic converteris eliminated, specifically by virtue of said part being bypassed viathe bypass line. This eliminates the cooling of the exhaust-gas stream,which is normally used as a carrier gas stream, which may occur owing tothermal inertia if said exhaust-gas stream were to flow through theexhaust-gas discharge system. The cooling of the carrier stream usedthat may occur in said part is eliminated likewise because the airstream used is first introduced into the exhaust-gas discharge systemdownstream of the further exhaust-gas aftertreatment systems andupstream of the at least one selective catalytic converter. Thisdistinguishes the carrier air stream from a secondary air flow which,according to the prior art, is fed in directly downstream of thecylinder outlet openings.

In the case of an internal combustion engine supercharged by means ofexhaust-gas turbocharging, in which the compressor of at least oneexhaust-gas turbocharger is arranged in the intake system and the bypassline branches off from the intake system downstream of said compressor,the charge air conducted through the bypass line is heated or intenselywarmed owing to compression, whereby the evaporation of the liquid ureaand the preparation thereof to form ammonia as reducing agent for the atleast one selective catalytic converter is assisted in an advantageousmanner.

In this way, the temperature of the carrier stream and the temperatureof the catalytic converter can be raised in a targeted manner, forexample in inner-city traffic, if the relatively low exhaust-gastemperatures hinder effective exhaust-gas aftertreatment by means of theexhaust-gas stream as a carrier gas stream.

It is also possible, for example by means of a heating device providedin the bypass line, to realize temperatures of approximately 150° C. to170° C. which may be considered to evaporate the urea solution, which isintroduced in aqueous form into the air, and generate ammonia.

The fact that the dosing device for the introduction of the ureasolution is provided in the bypass line also leads to advantages interms of the structural design of the exhaust-gas discharge system,because the arrangement of the dosing device in the bypass line makes itpossible for the selective catalytic converter, and possibly the furtherexhaust-gas aftertreatment systems, to be arranged in a close-coupled ormore close-coupled manner.

If the exhaust-gas temperatures increase to a critical level owing tothe present operation of the internal combustion engine, for example tosuch an extent that ammonia which is absorbed in the catalytic converterand which serves as reducing agent is released in uncontrolled fashionowing to an excessively high catalytic converter temperature and couldpass via the exhaust-gas discharge system into the environment, theexhaust gas can be cooled by virtue of the bypass line being opened andair being admixed, whereby the exhaust gas temperature and the catalyticconverter temperature may be lowered.

The first sub-object that is to say the provision of an internalcombustion engine which is optimized with regard to the operation of theat least one selective catalytic converter, is achieved by means of theinternal combustion engine.

For effective exhaust-gas aftertreatment, it is generally necessary formultiple exhaust-gas aftertreatment systems to be provided, for whichreason an oxidation catalytic converter is provided for theaftertreatment of the carbon monoxides and the unburned hydrocarbons.Said at least one further exhaust-gas aftertreatment system is arrangedin the exhaust-gas discharge system upstream of the at least oneselective catalytic converter.

A close-coupled arrangement of the oxidation catalytic converter betterenables fast heating of the oxidation catalytic converter, or basicallythat the operating temperature is attained and maintained. The oxidationprocesses that take place in the oxidation catalytic converter can beutilized to raise the exhaust-gas temperatures upstream of the at leastone SCR catalytic converter.

Further advantageous embodiments of the internal combustion engineaccording to the subclaims will be explained below.

Embodiments of the internal combustion engine may be advantageous inwhich a mixer is provided in the bypass line downstream of the dosingdevice.

For effective exhaust-gas aftertreatment, the ammonia that is producedby means of aqueous urea solution and which serves as reducing agentshould be adequately mixed with the carrier stream, that is to say theair. As homogeneous as possible an air-ammonia mixture shouldadvantageously be formed and flow through the at least one selectivecatalytic converter.

Embodiments of the internal combustion engine may be also advantageousin which a heater is provided in the bypass line upstream of the dosingdevice.

By means of a heater, the temperatures of the air which serves ascarrier gas can be raised, and thus the air temperatures for theevaporation of the aqueous urea solution can be generated. The heateradvantageously comprises a heatable grate or mesh through which the airflows. The grate or mesh serves for heating the air and cansimultaneously generate turbulence which assists the mixing of air andreducing agent downstream in the bypass line.

Embodiments of the internal combustion engine may be advantageous inwhich, upstream of the dosing device, there is provided a pump whichdraws in ambient air and delivers said ambient air into the bypass line.It must be considered here that charge air is extracted from the intakesystem via the bypass line, wherein the extracted charge air is, ineffect, omitted from the charge exchange, that is to say can no longerform a part of the cylinder fresh charge or charge air to be provided bythe intake system. This need not lead to potential issues; in particularneed not lead to an impaired charge exchange or impaired efficiency,under operating circumstances. For example, in the case of anapplied-ignition engine operated in the part-load range, it may readilybe possible, by means of reduced throttling of the intake air, for theextracted charge air to be provided by excess intake air. However, ifthe same applied-ignition engine is operated at higher loads or at fullload, that is to say is completely dethrottled or almost dethrottled, noexcess air can be drawn in, and the air extracted from the intake systemfor the bypass line is in fact omitted from the charge exchange. It isthen the intention for the pump to relieve the burden on the intakesystem by acting as an air delivery means for the bypass line, the pumpthen serving for feeding ambient air into the bypass line.

Said embodiment is suitable in particular for hybrid drives whichcomprise not only the internal combustion engine but also an electricmachine which can be connected in terms of drive to the internalcombustion engine and which receives power from the internal combustionengine or which, as a switchable auxiliary drive, additionally outputspower. An electrically operated pump may then be supplied withelectrical current from the electric machine or from the associatedbattery.

Embodiments of the internal combustion engine may be advantageous inwhich, downstream of the dosing device, there is provided a catalyticconverter for the catalytic assistance of the hydrolysis of isocyanicacid.

Whereas the urea solution is, with a supply of energy, split intoammonia (NH₃) and isocyanic acid (HNCO) in a thermolytic reaction, theisocyanic acid (HNCO) can be hydrolyzed in the presence of water (H₂O)to form ammonia (NH₃) and carbon dioxide (CO₂).

According to the present embodiment, a catalytic converter for thecatalytic assistance of the hydrolysis of isocyanic acid is provideddownstream of the dosing device.

Embodiments of the internal combustion engine may be advantageous inwhich the selective catalytic converter arranged downstream of theoxidation catalytic converter in the exhaust-gas discharge system isformed integrally with a particle filter as a combined exhaust-gasaftertreatment system.

Combined exhaust-gas aftertreatment systems have advantages with regardto the space requirement thereof. The selective catalytic converter andthe particle filter may share a common carrier substrate. The oxidationcatalytic converter is arranged upstream of and spaced apart from thecombined exhaust-gas aftertreatment system. In this way, disadvantageousexcessive heating of the selective catalytic converter owing toexcessively high temperatures of the oxidation catalytic converter canbe reduced.

Embodiments of the internal combustion engine may be also advantageousin which a particle filter as a further exhaust-gas aftertreatmentsystem is arranged in the exhaust-gas discharge system upstream of theat least one selective catalytic converter, the oxidation catalyticconverter being arranged upstream of the particle filter and the bypassline issuing into the exhaust-gas discharge system between the particlefilter and the at least one selective catalytic converter.

Embodiments of the internal combustion engine may be advantageous inwhich a control element is provided by means of which the air flow rateconducted through the bypass line can be adjusted.

The control element may be a valve, a slide, a flap or the like. Saidcontrol element may be electrically, hydraulically, pneumatically,mechanically or magnetically actuable, optionally controlled by means ofthe engine controller, and may be designed to be switchable, that is tosay adjustable, in two-stage, multi-stage or continuously variablefashion.

Embodiments of the internal combustion engine may be advantageous inwhich at least one exhaust-gas turbocharger is provided, the compressorof the at least one exhaust-gas turbocharger being arranged in theintake system, and the turbine of the at least one exhaust-gasturbocharger being arranged in the exhaust-gas discharge system.

The advantages of an exhaust-gas turbocharger for example in relation toa mechanical charger may be that no mechanical connection fortransmitting power exists between the charger and internal combustionengine. While a mechanical supercharger draws the energy for driving itfrom the internal combustion engine, the exhaust-gas turbochargerutilizes the exhaust-gas energy of the hot exhaust gases.

The energy imparted to the turbine by the exhaust-gas flow is utilizedfor driving a compressor which delivers and compresses the charge airsupplied to it, whereby supercharging of the cylinders is achieved. Acharge-air cooling arrangement may be provided, by means of which thecompressed combustion air is cooled before it enters the cylinders.

Supercharging serves primarily to increase the power of the internalcombustion engine. Supercharging is however also a suitable means forshifting the load collective toward higher loads for the same vehicleboundary conditions, whereby the specific fuel consumption can belowered.

A torque drop is often observed when a certain engine rotational speedis undershot. It is sought, using a variety of measures, to improve thetorque characteristic of a supercharged internal combustion engine. Thisis achieved for example by means of a small design of the turbine crosssection and simultaneous provision of an exhaust-gas blow-off facility.Such a turbine is also referred to as a wastegate turbine. If theexhaust-gas mass flow exceeds a critical value, then by opening ashut-off element, a part of the exhaust-gas flow is, within the courseof the so-called exhaust-gas blow-off, conducted via a bypass line pastthe turbine or the turbine impeller.

The torque characteristic of a supercharged internal combustion enginemay furthermore be improved by means of multiple turbochargers arrangedin parallel or in series, that is to say by means of multiple turbinesarranged in parallel or in series.

The turbine may furthermore be equipped with a variable turbinegeometry, which permits a more precise adaptation to the respectiveoperating point of the internal combustion engine by means of anadjustment of the turbine geometry or of the effective turbine crosssection. Here, adjustable guide blades for influencing the flowdirection may be arranged in the inlet region of the turbine. Incontrast to the rotor blades of the rotating rotor, the guide blades donot rotate with the shaft of the turbine.

If the turbine has a fixed, invariable geometry, the guide blades may bearranged in the inlet region so as to be not only stationary but ratheralso completely immovable, that is to say rigidly fixed. In contrast, inthe case of a variable geometry, the guide blades may be duly alsoarranged so as to be stationary but not so as to be completelyimmovable, rather so as to be rotatable, such that the flow approachingthe rotor blades can be influenced.

It is sought to arrange the turbine of an exhaust-gas turbocharger asclose as possible to the outlet of the internal combustion engine inorder thereby to be able to optimally utilize the exhaust-gas enthalpyof the hot exhaust gases, which is determined significantly by theexhaust-gas temperature and the exhaust-gas pressure, and to betterenable a fast response behavior of the turbocharger.

In this connection, it is therefore also sought to minimize the thermalinertia of the exhaust-gas discharge system between the outlet and theturbine, which can be achieved by reducing the mass and the length ofsaid part.

In this connection, embodiments of the internal combustion engine may betherefore also advantageous in which the turbine is arranged in theexhaust-gas discharge system upstream of the at least one furtherexhaust-gas aftertreatment system.

In the case of internal combustion engines with exhaust-gasturbocharging, embodiments may be advantageous in which the bypass linebranches off from the intake system downstream of the compressor of theat least one exhaust-gas turbocharger.

In the case of an internal combustion engine supercharged by means ofexhaust-gas turbocharging, in which the compressor of at least oneexhaust-gas turbocharger is arranged in the intake system and the bypassline branches off from the intake system downstream of said compressor,the charge air conducted through the bypass line is heated or intenselywarmed owing to compression, whereby the evaporation of the liquid ureaand the preparation thereof to form ammonia as reducing agent for the atleast one selective catalytic converter is assisted in an advantageousmanner.

In this way, the temperature of the carrier stream and the temperatureof the catalytic converter can be raised in a targeted manner, forexample in inner-city traffic, if the relatively low exhaust-gastemperatures hinder effective exhaust-gas aftertreatment by means of theexhaust-gas stream as a carrier gas stream.

In the case of internal combustion engines in which a charge-air coolingarrangement is provided downstream of the compressor in order to coolthe charge air, which has been compressed by means of the compressor,before said charge air enters the cylinders, embodiments may beadvantageous in which the bypass line branches off from the intakesystem upstream of said charge-air cooler.

In conjunction with an exhaust-gas turbocharging arrangement,embodiments of the internal combustion engine may be advantageous inwhich an additional feed line issues into the bypass line downstream ofthe compressor of the at least one exhaust-gas turbocharger, in whichfeed line there is arranged a pump which draws in ambient air anddelivers said ambient air into the bypass line.

That which has already been stated with regard to the use of a pumpapplies analogously. The pump serves for the provision of additionalair, optionally from the environment, and thus for the at least partialcompensation of the charge air that is extracted from the intake system.

Here, embodiments of the internal combustion engine may be advantageousin which the additional feed line issues into the bypass line so as toform a junction point, there being provided at the junction point acontrol element by means of which the charge-air flow rate conductedthrough the compressor of the at least one exhaust-gas turbocharger andthe ambient-air flow rate drawn in through the additional feed line canbe adjusted. That which has already been stated in conjunction with acontrol element applies here.

By means of the control element, the overall air stream conducted viathe bypass line can be generated by mixing of the two partial airstreams. The temperature and the pressure of the two partial air streamsdiffer, such that mixing of the two partial air streams may for examplealso be utilized to adjust the temperature of the overall air streamflowing through the bypass line.

The second sub-object, that of specifying a method for operating aninternal combustion engine of an above-stated type, is achieved by meansof a method for operating an internal combustion engine having a controlelement for the adjustment of the air flow rate conducted through thebypass line, in which method the bypass line is opened in order tosupply ammonia as reducing agent to the at least one selective catalyticconverter.

That which has already been stated with regard to the internalcombustion engine also applies to the method according, for which reasonreference is generally made at this juncture to the statements made withregard to the internal combustion engine.

Method variants may be advantageous in which the bypass line is openedif the exhaust-gas temperature T_(exhaust gas) is lower than apredefinable minimum exhaust gas temperature T_(exhaust gas, min).

The exhaust-gas temperature in the catalytic converter, at the inletinto the catalytic converter or at other locations in the exhaust-gasdischarge system may be used as reference exhaust-gas temperatureT_(exhaust gas, min).

Embodiments of the method may be advantageous in which the exhaust-gastemperature T_(exhaust gas) is determined mathematically. Themathematical determination of the exhaust-gas temperature is carried outby means of simulation, for which use is made of models known from theprior art, for example dynamic heat models and kinetic models fordetermining the reaction heat generated during the combustion. As inputsignals for the simulation, operating parameters of the internalcombustion engine which may be already available, that is to say whichhave been determined for other purposes.

The simulation calculation is characterized in that no furthercomponents, in particular no sensors, need be provided in order todetermine the exhaust-gas temperature, which is expedient with regard tocosts. It is however a disadvantage that the exhaust-gas temperaturedetermined in this way is merely an estimated value, which can reducethe quality of the control or regulation.

For the estimation of an exhaust-gas temperature T_(exhaust gas) at onelocation in the exhaust-gas discharge system, use may be made of theexhaust-gas temperature at another location in the exhaust-gas dischargesystem, which is for example also detected by measurement by means of asensor.

Embodiments of the method may be advantageous in which the exhaust-gastemperature T_(exhaust gas) is directly detected by measurement by meansof a sensor.

The detection of a temperature by measurement provides more accuratetemperature values, but may be difficult. This applies for example tothe detection of the temperature of an exhaust-gas aftertreatment systemby measurement, in which the lack of a possibility of arranging atemperature sensor in the exhaust-gas aftertreatment system can posepotential issues.

In contrast, the detection of the exhaust-gas temperature in an exhaustline by measurement may not pose difficulties.

Nevertheless, method variants may be advantageous in which the bypassline is opened if the exhaust-gas temperature T_(exhaust gas) at the atleast one selective catalytic converter is lower than a predefinableminimum exhaust-gas temperature T_(exhaust gas, min). Here, theexhaust-gas temperature at the catalytic converter may be equated withthe catalytic converter temperature T_(SCR), i.e. the componenttemperature, and vice versa.

A further sub-object of specifying a method for operating an internalcombustion engine of an above-stated type, is achieved by means of amethod for operating an internal combustion engine having a turbochargerwith a turbine positioned in the engine exhaust, a selective catalyticreducer (SCR) positioned downstream of the turbine and a compressordriven by the turbine comprising supplying compressed air from thecompressor to the engine. The method comprises injecting a ureareductant into the SCR through a dosing device to reduce NOx andcontrolling temperature of the reductant within a predetermined range byportioning an air flow into the reductant within a predetermined rangeby portioning an air flow into the reductant between a portion ofcompressed air and ambient air.

Embodiments of the method may be advantageous in which the engine torqueadjustment comprises adjusting exhaust flow across the turbine. Further,a wastegate may be coupled to the engine exhaust and positioned inparallel with the turbine and a wastegate control valve controllingexhaust flow through said wastegate wherein said engine torqueadjustment comprises adjusting said wastegate valve.

Embodiment of the method may be advantageous in which a heat exchangeris positioned downstream of the compressor wherein a portion of thecompressed air supplied across the dosing device is supplied fromupstream the heat exchanger.

Method variants may be advantageous wherein the predeterminedtemperature is in a range between 150 to 170 degrees centigrade.

Another sub-object is a method comprising supplying compressed air to anengine from a compressor driven by a turbine coupled to exhaust from theengine for controlling temperature of a reductant dosing deviceinjecting a reductant into a catalyst coupled to an exhaust. Controllingthe temperature of the reductant to be within a predetermined range bypassing over the reductant one or more of the following: a combinationof compressed air and ambient air or a combination of the exhaustupstream and downstream of the turbine.

Embodiments of the method may be advantageous in which compressed air issupplied to the engine to achieve a desired torque.

Embodiments of the method may be advantageous in which a combination ofcompressed and ambient air is passed over said reductant for saidtemperature control, increasing said compressed air and decreasing saidambient air in said combination increases said temperature, anddecreasing said compressed air and increasing said ambient air decreasessaid temperature.

Further, the method may correct for engine torque to compensate forchanges in said torque.

Method variants may be advantageous in which the correction of thetorque may be enacted by changing one or more of the following: changingposition of a throttle controlling flow of said ambient air into saidengine, changing timing of injecting fuel into said engine, and/orchanging said exhaust flow upstream of said turbine.

Method variants may be advantageous wherein said temperature controlfurther comprises passing said combination of said exhaust upstream anddownstream of the turbine over the reductant when the torque correctionis unable to fully correct for changes in the torque.

Embodiments of the method may be advantageous wherein the combination ofthe exhaust upstream and downstream of the turbine is passed over thereductant to achieve the temperature control, increasing the exhaustupstream of the turbine and decreasing the exhaust downstream of theturbine increase the temperature, and decreasing the exhaust upstream ofthe turbine and increasing the exhaust downstream of the turbinedecreases the temperature.

Method variants may be advantageous wherein correcting engine torque tocompensate for changes in said torque by the passing the exhaustupstream of said turbine over the reductant.

Method variants may be advantageous wherein said torque correctioncomprises changing one or more of the following: changing position of athrottle controlling flow of the ambient air into the engine, changingtiming of injecting fuel into the engine, and/or changing the compressedair flow.

Method variants may be advantageous wherein the temperature controlfurther comprises passing the combination of the compressed air and theambient air over the reductant when the torque correction is unable tofully correct for changes in the torque.

Embodiments may be advantageous wherein the catalyst is a selectivereduction catalyst.

Embodiments may be advantageous wherein a dosing element to inject thereductant is positioned in a bypass line coupled to an inlet of saidcatalyst.

Embodiments may be advantageous wherein the compressed air and theambient air may be coupled to an air line coupled to the bypass line andfurther comprising a control element coupled to said air line forcontrolling an amount of compressed air and an amount of the ambient airentering said dosing line to control said temperature.

Method variants may be advantageous wherein the exhaust upstream of theturbine and downstream of the turbine may be coupled to a line coupledto the bypass line and further comprising a control valve coupled tosaid line for controlling an amount of said exhaust upstream of theturbine and an amount of said exhaust downstream of the turbine enteringsaid bypass line to control said temperature.

Embodiments may be advantageous wherein the reductants is urea and thepredetermined temperature rang enables the conversion of the urea toammonia.

A further sub-object is a method comprising injecting a reductant into acatalyst coupled to the exhaust and passing a mixture of compressed air,exhaust from upstream of a turbine and exhaust from downstream of aturbine to the injected reductant.

Embodiments may be advantageous wherein the method further comprisesadjusting relative amounts of the compressed air, upstream exhaust, anddownstream exhaust in the mixture responsive to temperature of thereductant.

Embodiments may be advantageous wherein adjusting the relative amountsincludes: during a first condition, adjusting relative amounts ofupstream and downstream exhaust responsive to temperature whilemaintaining the compressed air amount in the mixture; and during asecond condition, adjusting the amount of compressed air whilemaintaining the relative amounts of upstream and downstream exhaust inthe mixture.

Method variants may be advantageous wherein the first condition andsecond condition may be selected responsive to compressor surge.

Method variants may be advantageous wherein the first condition andsecond condition may be mutually exclusive.

In one example, a method for controlling an engine having a turbochargerwith a turbine positioned in the engine exhaust, a Selective CatalyticReducer (SCR) positioned downstream of the turbine, and a compressordriven by the turbine, comprising: supplying compressed air from thecompressor to the engine to achieve a torque; injecting a urea reductantinto the SCR through a dosing device to reduce NOx; controllingtemperature of said dosing device to be within a predetermined range forconversion of said urea to ammonia by one or more of the following:portioning an air flow across said dosing device between a portion ofsaid compressed air and another portion of ambient air; or, portioningan exhaust flow across said dosing device between a portion of saidexhaust upstream and downstream of the turbine; adjusting engine torqueto compensate for said portioning of said compressed air; and when saidportioning airflow is used for said temperature control and said enginetorque adjusting reaches a threshold, then change from said portioningairflow to said portioning exhaust flow for said temperature control.

The method may further comprise changing from said portioning exhaustflow for said temperature control to said portioning airflow for saidtemperature control when said said portioning exhaust flow is used forsaid temperature control and said engine torque adjusting reaches saidthreshold. In examples, said compressed air is supplied to the enginethrough a cooler downstream of the compressor, and said portioning saidcompressed air comprises portioning said compressed air upstream of saidcooler and said torque adjustment may comprises one or more of thefollowing: adjusting position of a throttle controlling an amount ofambient air entering the engine; controlling timing of injecting fuelinto the engine; controlling timing of igniting spark plugs coupled to acombustion chamber of the engine; controlling said portioning of saidcompressed air; and/or controlling said portioning of said exhaustupstream of the turbine.

FIG. 1 schematically shows, in the form of a diagrammatic sketch, afirst embodiment of the internal combustion engine 1.

The internal combustion engine 1 has an intake system 2 for the supplyof charge air and has an exhaust-gas discharge system 3 for thedischarge of the exhaust gases. An exhaust-gas turbocharger 4 isprovided for supercharging purposes. The compressor 4 a of theexhaust-gas turbocharger 4 is arranged in an intake line 2 a of theintake system 2, and the turbine 4 b of the exhaust-gas turbocharger 4is arranged in an exhaust line 3 a of the exhaust-gas discharge system3.

Various systems 5, 5 a, 6, 6 a, 7 for exhaust-gas aftertreatement may beprovided downstream of the turbine 4 b.

Two selective catalytic converters 6, 7 may be provided for thereduction of nitrogen oxides, wherein a further exhaust-gasaftertreatment system 5 is arranged upstream of said two selectivecatalytic converters 6, 7. In the present case, the further exhaust-gasaftertreatment system 5 is an oxidation catalytic converter 5 a, whereinthe selective catalytic converter 6, which is arranged downstream of theoxidation catalytic converter 5 a in the exhaust line 3 a, is formedintegrally with a particle filter 6 a as a combined exhaust-gasaftertreatment system. A second selective catalytic converter 7 isarranged in the exhaust-gas discharge system 3 downstream of the firstselective catalytic converter 6 which is formed integrally with theparticle filter 6 a.

A bypass line 8 branches off from the intake system 2 downstream of thecompressor 4 a and issues into the exhaust-gas discharge system 3between the oxidation catalytic converter 5 a and the combinedexhaust-gas aftertreatment system comprising the first selectivecatalytic converter 6 and the particle filter 6 a.

A dosing device 9 is provided for introducing liquid urea into thebypass line 8 in order to be able to generate, that is to say provide,ammonia which serves as reducing agent for the selective catalyticconverters 6, 7. A mixer 10 is provided in the bypass line 8 downstreamof the dosing device 9, which mixer mixes the ammonia, which serves asreducing agent, with the charge air in order to form as homogeneous anair-ammonia mixture as possible, which flows through the catalyticconverters 6, 7.

Likewise arranged in the bypass line 8 is a control element 11 whichserves for adjusting the air flow rate conducted through the bypass line8. A pivotable flap 11 a may serve as a control element 11.

FIG. 2 schematically shows, in the form of a diagrammatic sketch, asecond embodiment of the internal combustion engine 1. It is sought toexplain only the differences in relation to the embodiment illustratedin FIG. 1, for which reason reference is otherwise made to FIG. 1. Thesame reference symbols have been used for the same components.

By contrast to the embodiment illustrated in FIG. 1, no combinedexhaust-gas aftertreatment system comprising a selective catalyticconverter and a particle filter is provided in the case of the internalcombustion engine 1 illustrated in FIG. 2. Instead, an oxidationcatalytic converter 5 a and a particle filter 6 a, as furtherexhaust-gas aftertreatment systems 5, may be arranged in the exhaust-gasdischarge system 3 upstream of a single selective catalytic converter 7.The oxidation catalytic converter 5 a is arranged upstream of theparticle filter 6 a, wherein the bypass line 8 issues into theexhaust-gas discharge system 3 between the particle filter 6 a and theselective catalytic converter 7.

Turning to FIGS. 3 a and 3 b an example method to control the dosingtemperature of the reductant is shown.

At 402 the method may determine the desired torque. The desired torquemay be determined from the engine speed, driver input, various sensors,etc.

At 404 the method may determine the desired boost pressure for thedesired torque at step 402.

At 406 the method may adjust the boost pressure to the boost pressuredesired determined at 404. The boost pressure may be adjusted to meetthe boost pressure desired by adjusting one or more of the following:the variable turbo nozzle, a wastegate valve (not shown) positioned inan exhaust wastegate line (not shown) in parallel with the turbine fordiverting a portion of exhaust flow across the turbine therebycontrolling exhaust flow through the turbine and boost. The controlelement also may be used to adjust boost by diverting air from thecompressor away from the engine air intake.

At 408 the method may determine the ambient temperature and thecompressor air temperature. For example, the temperatures may bemeasured by sensors, determined from engine operating parameters such asboost pressure, or may be estimated by a simulation calculation.

At 410 the method may determine the dosing temperature. The dosingtemperature may be determined for the ambient temperature and thecompressor air temperature determined at 408. Further the dosingtemperature may be determined by a sensor.

At 412 the method may determine if the dosing temperature is below aminimum threshold temperature. If no, the method may proceed to 414 andfurther determine if the dosing temperature is above a maximum thresholdtemperature. If no, the method may continue to 416 and no further stepsmay be needed. If yes at 414, the method may proceed to 418 and decreasethe control element to decrease air flow from the compressor andincrease the ambient air flow across the dosing device therebydecreasing its temperature.

If yes at 412, the method may increase the control element to increasethe air flow from the compressor and decrease the ambient air flowacross the dosing device to increase its temperature.

From either 418 or 420 the method may proceed to 422. At 422 the methodmay determine a change in torque based on the change to the air flowfrom the compressor in either step 418 or 420.

At 424 the method may determine the allowed change in torque. Theallowed change in torque may be determined based on engine load, tip in,engine temperature, etc. For example, at low load the allowed change intorque may have a greater range and the method may give more weight totemperature regulation of the bypass line. As another example, at highload or medium load and tip in, the allowed change in torque may have alower range and the method may give a lower weight to temperatureregulation of the bypass line.

At 426 the method may determine if the change in torque is greater thanthe allowed change in torque. If no, the method may proceed to 428 andrejoin the method at 412.

If yes, the method may proceed to 430 and determine if the change intorque is within a threshold to adjust the change in torque by throttleangle TA and/or injection timing. If no, the change in torque is outsidethe threshold the method may continue to 442. If yes, the method mayproceed to 432 and adjust the TA and/or injection timing beforerejoining the method at 426.

At 442 the method may determine if the temperature range thresholds maybe changed to allow for torque correction.

If yes, the method may proceed to 436 and change the temperature rangethresholds. At 438 the method may increment the wastegate valve, turbinevanes, or control element to change the engine torque. The method maythen continue to 440 and rejoin the method at 412 to further changecompressor and ambient airflow to correct dosing temperature with thenow allowed greater range of permitted temperatures.

If no at 442, the method may end.

A further potential approach include the internal combustion enginecomprising an intake system for the supply of charge air, an exhaust gasdischarge system for the discharge of the exhaust gases with at leastone selective catalytic converter being arranged, as a further exhaustgas aftertreatment system, in the exhaust gas discharge system upstreamof the at least on selective catalytic converter, further comprises abypass line which branches off from the intake system and issues intothe exhaust gas discharge system between the oxidation catalyticconverter and the at least one selective catalytic converter, a dosingdevice being provided for introducing liquid urea as a reducing agentfor the at least one selective catalytic converter into the bypass line.

A method for controlling an engine having a selective catalytic reducer(SCR) coupled to an engine exhaust comprising supplying compressed airto the engine to achieve a desired torque, injecting a reductant intothe SCR, controlling a temperature of the reductant between a portion ofsaid compressed air and ambient, and adjusting engine torque tocompensate for said portioning of said compressed air.

A method for controlling an engine having a turbocharger with a turbinepositioned in the engine exhaust, a selective catalytic reducer (SCR)positioned downstream of the turbine and a compressor driven by theturbine comprising supplying compressed air from the compressor to theengine, injecting a urea reductant into the SCR through a dosing deviceto reduce NOx, controlling temperature of the dosing device to be withina predetermined range for conversion of the urea to ammonia byportioning an air flow across the dosing device between a portion ofsaid compressed air and another portion of ambient air, and adjustingengine torque to compensate for said portioning of the compressed air.

Turning to FIG. 4 a schematic of a compressor bypass line connected to aturbine bypass line is shown. The internal combustion engine 1 has anintake system 2 for the supply of charge air and has an exhaust-gasdischarge system 3 for the discharge of the exhaust gases. Anexhaust-gas turbocharger 4 is provided for supercharging purposes. Thecompressor 4 a of the exhaust-gas turbocharger 4 is arranged in anintake line 2 a of the intake system 2, and the turbine 4 b of theexhaust-gas turbocharger 4 is arranged in an exhaust line 3 a of theexhaust-gas discharge system 3. A wastegate 26 may be coupled to theengine exhaust and positioned in parallel with the turbine and awastegate control valve 28 may be positioned in the wastegate 26controlling exhaust flow through said wastegate.

Various systems 5, 5 a, 6, 6 a, 7 for exhaust-gas aftertreatment may beprovided downstream of the turbine 4 b.

Two selective catalytic converters 6, 7 may be provided for thereduction of nitrogen oxides, wherein a further exhaust-gasaftertreatment system 5 is arranged upstream of said two selectivecatalytic converters 6, 7. In the present case, the further exhaust-gasaftertreatment system 5 is an oxidation catalytic converter 5 a, whereinthe selective catalytic converter 6, which is arranged downstream of theoxidation catalytic converter 5 a in the exhaust line 3 a, is formedintegrally with a particle filter 6 a as a combined exhaust-gasaftertreatment system. A second selective catalytic converter 7 isarranged in the exhaust-gas discharge system 3 downstream of the firstselective catalytic converter 6 which is formed integrally with theparticle filter 6 a.

A bypass line 8 branches off from the intake system 2 downstream of thecompressor 4 a, upstream of the turbine, and downstream of the turbineand issues into the exhaust-gas discharge system 3 between the oxidationcatalytic converter 5 a and the combined exhaust-gas aftertreatmentsystem comprising the first selective catalytic converter 6 and theparticle filter 6 a. An additional feed line issues into the bypass linedownstream of the compressor of the at least one exhaust-gasturbocharger, in which feed line there is arranged a pump 20 which drawsin ambient air and delivers said ambient air into the bypass line.Further, a heat exchanger 30 may be positioned downstream of thecompressor and the bypass line 8 may branch off from upstream the heatexchanger 30.

A dosing device 9 (e.g., an injector) is provided for introducing liquidurea into the bypass line 8 in order to be able to generate, that is tosay provide, ammonia which serves as reducing agent for the selectivecatalytic converters 6, 7. A mixer 10 is provided in the bypass line 8downstream of the dosing device 9, which mixer mixes the ammonia, whichserves as reducing agent, with the charge air in order to form ashomogeneous an air-ammonia mixture as possible, which flows through thecatalytic converters 6, 7. A heater 22 may be provided in the bypassline upstream of the dosing device. A catalytic converter 24 for thecatalytic assistance of the hydrolysis of isocyanic acid may be provideddownstream of the dosing device.

Likewise arranged in the bypass line 8 is a control element 11 whichserves for adjusting the air flow rate conducted through the bypass line8 from the compressor bypass line and the ambient air. A pivotable flap11 a may serve as a control element 11. A diverter valve 12 is arrangedin the bypass line 8 which serves for adjusting the exhaust gas flowrate conducted through the bypass line 8 from the first and secondexhaust bypass line segments. A pivotable flap 12 a may serve as thediverter valve 12.

FIG. 5 schematically shows, in the form of a diagrammatic sketch, thecompressor bypass line connected to a turbine bypass line of theinternal combustion engine 1. It is sought to explain only thedifferences in relation to the embodiment illustrated in FIG. 4, forwhich reason reference is otherwise made to FIG. 4. The same referencesymbols have been used for the same components.

By contrast to the embodiment illustrated in FIG. 4, no combinedexhaust-gas aftertreatment system comprising a selective catalyticconverter and a particle filter is provided in the case of the internalcombustion engine 1 illustrated in FIG. 4. Instead, an oxidationcatalytic converter 5 a and a particle filter 6 a, as furtherexhaust-gas aftertreatment systems 5, may be arranged in the exhaust-gasdischarge system 3 upstream of a single selective catalytic converter 7.The oxidation catalytic converter 5 a is arranged upstream of theparticle filter 6 a, wherein the bypass line 8 issues into theexhaust-gas discharge system 3 between the particle filter 6 a and theselective catalytic converter 7.

Turning to FIGS. 6 a, 6 b and 6 c an example method for controllingreductant dosing temperature is shown.

At 602 the method may determine the desired torque. The desired torquemay be determined from the engine speed, driver input, various sensors,etc.

At 604 the method may determine the desired boost pressure for thedesired torque at step 602.

At 606 the method may adjust the boost pressure to the boost pressuredesired determined at 604. The boost pressure may be adjusted to meetthe boost pressure desired by adjusting one or more of the following:the variable turbo nozzle, or a wastegate valve (not shown) positionedin an exhaust wastegate line (not shown) in parallel with the turbinefor diverting a portion of exhaust flow across the turbine therebycontrolling exhaust flow through the turbine and boost. The controlelement also may be used to divert a portion of air from the compressoraway from the engine air intake and change torque. Further, the divertervalve also may be used to reduce exhaust airflow across the turbine andchange engine torque.

At 608 the method may determine the ambient temperature and thecompressor air temperature. For example, the temperatures may bemeasured by sensors, determined from engine operating parameters such asboost pressure, or may be estimated by a simulation calculation.

At 610 the method may determine the dosing temperature. The dosingtemperature may be determined for the ambient temperature and thecompressor air temperature determined at 408. Further the dosingtemperature may be determined by a sensor.

At 612 the method may determine if the dosing temperature is below aminimum threshold temperature. If no, the method may proceed to 614 andfurther determine if the dosing temperature is above a maximum thresholdtemperature. If no, the method may continue to 616 and no further stepsmay be needed. If yes at 614, the method may proceed to 618 and decreasethe control element to decrease air flow from the compressor andincrease the ambient air flow across the dosing device therebydecreasing its temperature.

If yes at 612, the method may increase the control element to increasethe air flow from the compressor and decrease the ambient air flowacross the dosing device to increase its temperature.

From either 618 or 620 the method may proceed to 622. At 622 the methodmay determine a change in torque based on the change to the air flowfrom the compressor in either step 618 or 620.

At 624 the method may determine the allowed change in torque. Theallowed change in torque may be determined based on engine load, tip in,engine temperature, etc. For example, at low load the allowed change intorque may have a greater range and the method may give more weight totemperature regulation of the bypass line. As another example, at highload or medium load and tip in, the allowed change in torque may have alower range and the method may give a lower weight to temperatureregulation of the bypass line.

At 626 the method may determine if the change in torque is greater thanthe allowed change in torque. If no, the method may proceed to 628 andrejoin the method at 612.

If yes, the method may proceed to 630 and determine if the change intorque is within a threshold to adjust the change in torque by throttleangle TA and/or injection timing. If no, the change in torque is outsidethe threshold the method may continue to 634. If yes, the method mayproceed to 632 and adjust the TA and/or injection timing beforerejoining the method at 626.

At 634 the method may determine if the temperature range thresholds maybe changed to allow for torque correction.

If yes, the method may proceed to 636 and change the temperature rangethresholds. At 638 the method may increment the wastegate valve, turbinevanes, or control element to change the engine torque. The method maythen continue to 640 and rejoin the method at 612 to further changecompressor and ambient air flow to correct dosing temperature with thenow allowed greater range of permitted temperatures.

If no at 634, the method may proceed to 642 on FIG. 6 c and determine ifthe reductant dosing temperature is below a minimum threshold. If yes,the method may proceed to 644 and increase the diverter valve toincrease the flow of exhaust gas through the first bypass line sectionand decrease the flow through the second bypass line section to increasetemperature across the dosing device. The method may then end.

If no at 642 the method may proceed to 646 and determine if thereductant dosing temperature is above a temperature threshold maximum.If no, the method may end. If yes, the method may proceed to 648 anddecrease the diverter valve to decrease the flow of exhaust gas throughthe first bypass line section and increase the flow of exhaust gasthrough the second bypass line section to decrease temperature acrossthe dosing device. The method may then end.

In the particular example described above with reference to FIGS. 6 a, 6b, and 6 c, temperature of the dosing device was first controlled byportioning airflow between compressed air and ambient air, and whenengine torque changed beyond and allowed change that could not beadjusted by TA or injector timing, the dosing temperature was correctedby portioning exhaust flow between upstream and downstream of theturbine. In another example of operation, the approach may be reversed.Temperature of the dosing device may first be controlled by portioningexhaust flow, and torque changes may then result in the temperaturebeing controlled by portioning airflow.

Further, the method may adjust the relative amounts of the compressedair, upstream exhaust, and downstream exhaust in the mixture responsiveto temperature of the reductant concurrently or mutually exclusively. Inone example, the method may adjust the relative amounts of thecompressed air and the upstream exhaust and downstream exhaustresponsive to the dosing temperature. Another example of the method mayadjust the amount of the compressed air while maintaining the amounts ofthe upstream exhaust and downstream exhaust responsive to the desiredtorque. Another example of the method may adjust the upstream exhaustand downstream exhaust while maintaining the compressed air amountresponsive to compressor surge.

It will be appreciated by those skilled in the art that although theinvention has been described by way of example with reference to one ormore embodiments it is not limited to the disclosed embodiments and thatalternative embodiments could be constructed without departing from thescope of the invention as defined by the appended claims.

The invention claimed is:
 1. An internal combustion engine comprising:an intake system including an intake line for the supply of charge air;an exhaust-gas discharge system for the discharge of exhaust gases; atleast one selective catalytic converter arranged in the exhaust-gasdischarge system for the reduction of nitrogen oxides; an oxidationcatalytic converter being arranged in the exhaust-gas discharge systemupstream of the at least one selective catalytic converter; wherein abypass line branches off from the intake system downstream of acompressor and issues into the exhaust-gas discharge system between theoxidation catalytic converter and the at least one selective catalyticconverter; a dosing injector being provided for introducing liquid ureaas a reducing agent for the at least one selective catalytic converterinto the bypass line; and an additional feed line issues into the bypassline to deliver ambient air into the bypass line and a control elementis coupled at a junction between the additional feed line and the bypassline to control an amount of compressed air and an amount of the ambientair entering said bypass line to control a temperature of the liquidurea.
 2. The internal combustion engine as claimed in claim 1, wherein amixer is provided in the bypass line downstream of the dosing injector.3. The internal combustion engine as claimed in claim 1, wherein,upstream of the dosing injector, there is provided a pump positioned inthe additional feed line which draws in the ambient air and deliverssaid ambient air into the bypass line.
 4. The internal combustion engineas claimed in claim 1, wherein, downstream of the dosing injector, thereis provided a catalytic converter for the catalytic assistance ofhydrolysis of isocyanic acid.
 5. The internal combustion engine asclaimed in claim 1, wherein the control element is configured to adjustan air flow rate conducted through the bypass line.
 6. The internalcombustion engine as claimed in claim 1, wherein the compressor is acompressor of an exhaust-gas turbocharger, the compressor of theexhaust-gas turbocharger being arranged in the intake system, and aturbine of the exhaust-gas turbocharger being arranged in theexhaust-gas discharge system.
 7. The internal combustion engine asclaimed in claim 1, wherein a heater is provided in the bypass lineupstream of the dosing injector to control the temperature of the liquidurea.
 8. A method for controlling an engine having a selective catalyticreducer (SCR) coupled to an engine exhaust comprising: supplyingcompressed air to the engine to achieve a desired torque; injecting areductant into the SCR; controlling temperature of said reductant withina predetermined range by portioning an air flow into said reductantbetween a portion of said compressed air and ambient air; and adjustingengine torque to compensate for said portioning of said compressed air.9. The method as claimed in claim 8 further comprising controlling thetemperature of said reductant by operating a heater within a bypassline.
 10. The method recited in claim 8 wherein said compressed air isprovided by an air pump.
 11. The method recited in claim 8 wherein saidportion of said compressed air is increased and said portion of saidambient air is decreased when said reductant temperature is less thansaid predetermined range.
 12. The method recited in claim 8 wherein saidportion of said compressed air is decreased and said portion of saidambient air is increased when said reductant temperature is greater thansaid predetermined range.
 13. The method recited in claim 8 wherein saidengine torque adjustment comprises adjusting one or more of thefollowing: throttle angle of a throttle blade positioned in an airintake of the engine, or fuel injection timing of fuel injectorsinjecting fuel into the engine.
 14. A method for controlling an enginehaving a turbocharger with a turbine positioned in the engine exhaust, aselective catalytic reducer (SCR) positioned downstream of the turbine,and a compressor driven by the turbine comprising: supplying compressedair from the compressor to the engine; injecting a urea reductant intothe SCR through a dosing injector to reduce NOx; controlling temperatureof said dosing injector to be within a predetermined range forconversion of said urea to ammonia by portioning an air flow across saiddosing injector between a portion of said compressed air and anotherportion of ambient air; and adjusting engine torque to compensate forsaid portioning of said compressed air.
 15. The method recited in claim14 wherein said engine torque adjustment comprises adjusting exhaustflow across said turbine.
 16. The method recited in claim 15 furthercomprising a wastegate coupled to the engine exhaust and positioned inparallel with the turbine and a wastegate valve controlling exhaust flowthrough said wastegate wherein said engine torque adjustment comprisesadjusting said wastegate valve.
 17. The method recited in claim 14further comprising a heat exchanger positioned downstream of thecompressor wherein said portion of said compressed air supplied acrosssaid dosing injector is supplied from upstream of said heat exchanger.18. The method recited in claim 14 wherein said predeterminedtemperature range is between 150 to 170 degrees Centigrade.
 19. Themethod recited in claim 14 wherein said ammonia reduces nitrogen oxideemissions in the SCR.